Yahoo Inc. and Microsoft Corp. are both stepping up efforts to challenge Google Inc.'s success in selling online advertisements linked to user searches.

On Wednesday Yahoo released the beta of an expansion to its existing Yahoo Publisher Network, which enables large Web sites such as CNN.com and ESPN.com to run Yahoo sponsor ads and receive revenue when users click on those ads. Now Yahoo is extending that opportunity to small and medium-sized Web publishers through a beta self-service platform that allows companies to choose what kind of ads they want to be placed on their sites, according to the company.

The beta will be tested with 2,000 invited publishers and is expected to be in full release by the end of the year, according to a Yahoo spokeswoman.

Through the self-service center, Web publishers such as Web log and e-commerce sites can choose not only ads linked contextually to the topic of their sites, but also ads in other topics that they think users might be interested in, which they choose from a scroll-down menu in a service called Y!Q Beta, according to Yahoo. They also can choose the look of the ads so it fits into their sites, and also block URLs (Uniform Resource Locators) from sponsors that might be competitive to their site.

The Yahoo Publisher Network self-service beta also provides access to other Yahoo products, such as "Add to My Yahoo." The "Add to My Yahoo" feature gives publishers the opportunity to promote and distribute their content on Yahoo via RSS (Really Simple Syndication), drive traffic back to their sites and develop repeat daily relationships with their readers, according to the company.

Microsoft, too, aims to snare more advertising dollars through its search engine on MSN.com, and is readying a new paid-search solution as part of its MSN adCenter platform, a Microsoft spokeswoman confirmed Wednesday.

Microsoft will debut a pilot of the paid-search offering, part of its adCenter online advertising platform, in France and Singapore beginning in October, she said.

The company first announced adCenter in March at the MSN Strategic Account Summit, positioning it as a way to help advertisers connect with their desired audience through the MSN network, according to a press release at the time of the announcement.

With the paid-search component of adCenter, Microsoft is looking to address what it thinks are several "pain points" with online advertising and paid search, such as the lack of rich targeting capabilities, lack of business intelligence reporting and lack of tools for smaller advertisers, according to the company.

The paid-search solution in adCenter will eventually give advertisers a self-service platform to plan, execute and adjust their online campaigns, according to Microsoft.

In addition to its plans to garner more ad revenue to battle Google, Microsoft also may emulate rival Google's matter-of-fact start page through work the company is doing in an MSN incubation project called Start.com.

The project, which can be found on the MSN Sandbox site that previews MSN prototypes and other ideas from the MSN team, offers a stripped-down start page rather than the current content-heavy MSN.com start page, according to the MSN Sandbox Web site. The page, which can be found at http://www.start.com/myw3b/, has a simple search toolbar, as well as headlines presented as simple text links with no photos or multimedia.

According to the Sandbox site, Start.com is an "experimental project" aimed at making the Web "faster, more organized and personal for consumers." The project was launched with start.com/1 in early March, followed by start.com/2 a few weeks later, and is now in its third incarnation with start.com/3, which went live on June 3.